1. Field of the Invention
The present invention relates generally to a process for the removal of carbonyl contaminants in hydrocarbon streams. More particularly the invention relates to the removal of carbonyl compounds from a stream containing at least aldehydes, ketones or esters. More particularly the invention relates to a removal process wherein the carbonyl compounds, including the aldehydes and ketones, undergo reactions in the presence of an acidic catalyst and at least, a part of the reaction products are adsorbed/absorbed on the catalyst.
2. Related Art
Linear olefins are isomerized to branched olefins in the presence of an acidic catalyst such as molecular sieves, silica-alumina, fluorinated alumina, etc. The tertiary olefins that are a product of the isomerization are useful as feed to a tertiary ether process or to an alkylation process.
When a stream containing both linear and branched olefins is fed to an etherification process the branched olefins preferentially react with an alcohol to produce the tertiary ether. In the case of isobutene and methanol the reaction product is methyl tertiary butyl ether (MTBE) and in the case of isopentene (isoamylene) and methanol the product is tertiary amyl methyl ether (TAME). Both ethers are useful as gasoline additives.
The unreacted linear olefins, either the normal butenes or normal pentenes, can be used in a cold acid alkylation process or may be isomerized to branched olefins and recycled back to the etherification process. In either case, the normal olefins from the initial etherification may contain trace amounts of the unreacted alcohol which act as catalyst inhibitor in the isomerization process or consume acid in cold acid alkylations. Aldehydes and ketones may be contained in other feedstreams to a skeletal isomerization process. For example, the C5 stream from a Fischer-Tropsch synthetic fuel process contains small amounts of acetone, propionaldehyde, methyl ethyl ketone and butylaldehyde as well as alcohols. These carbonyl compounds render molecular sieve skeletal isomerization catalysts, such as zeolites, e.g., ferrierite, useless after only a few hours on stream. In an integrated process for etherification and isomerization as disclosed in U.S. Pat. No. 5,210,327 and U.S. Pat. No. 5,276,212, the linear olefins are treated to remove the alcohol, water and nitrogen compounds prior to the isomerization. The alcohol and nitrogen compounds are removed by adsorption on zeolitic molecular sieves by a process disclosed in U.S. Pat. No. 4,814,517. Any acetone or acetonitrile in the feed is removed by a water wash prior to the etherification.
In the present process the carbonyl compounds, comprising at least aldehydes or ketones, contact the acidic material at a temperature high enough to cause the reaction of the carbonyl compounds on contact with the acidic material and adsorption onto the acidic material which is regenerated or replaced after the acidic material declines in activity.
One embodiment of the present invention comprises a process for treating feeds to an olefin isomerization process to remove the carbonyl compounds in which a feed stream comprising a mixed hydrocarbon stream containing linear and branched C5 olefins along with small amounts of aldehydes, ketones and alcohols. The feed is passed over an acidic catalyst, such as xcfx84-alumina at moderately elevated temperatures in vapor phase to react the carbonyl compounds with themselves and the olefins. At least a part of the reaction products are deposited onto the alumina and the feed is then passed over an olefin skeletal isomerization catalyst to convert linear olefins to branched olefins. Some of the reaction products may stay on the acidic material or desorb into hydrocarbon vapor phase, depending on the temperature of the acidic material catalyst bed, molecular weight of reaction products and type of the reaction products whether olefins, olefinic alcohols or diols. Particularly the normal pentenes are converted to isoamylenes.
As used herein the term xe2x80x9cabsorbedxe2x80x9d and its variations mean a physical intervention of the sorbed material into the absorbent without chemical change of the absorbed material and hence condensed phase (multimolecular layers) can be formed on the surface of solid materials such as vapor condensation on a solid surface. xe2x80x9cAdsorbedxe2x80x9d and its variations mean a bonding of the sorbed material onto the surfaces of the adsorbent (chemisorption) and hence chemisorption does not go beyond the formation of a monolayer on the surface.